Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing or whistle(吹口哨) when you are happy.

    Some scientists believe that birds do sing some of time just because they are happy. However, they sing most of the time for a very different reason. Their singing is actually a warning to other birds to stay out of their territory.

    Do you know what a “territory” is? A territory is an area that an animal, usually the male, claims as its own. Only he and his family are welcome there. No other families of the same species(物种) are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and threaten you, you might shout. Probably this would be enough to frighten him away.

    If so, you have actually frightened the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting(筑巢) season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird's song, and it is usually enough to keep an outsider away.

    Birds sing loudest in the spring when they are trying to attract a mate（配偶）and warn others not to enter the territory of theirs.

    You can see that birds have a language all their own. Most of it has something to do with attracting mates and setting up territories.

    On the third Sunday in June, Americans take time to recognize and thank a special person in the family -fathers! Father's Day celebrates the importance of fathers, young and old and the men thought of as father figures.

    The words "the child is father of the man" come from William Wordsworth's poem My Heart Leaps Up. "It means people's personalities form when they are children. They will most likely have the same qualities as an adult that they had as a child.

    Used in everyday speech, one could say, "In his case, the child was father of the man; he loved nature as a child and now works as a botanist(植物学家)".

    Let's say you want to tell a child a story about something that happened long before they were born. You could say it happened when they “were just a twinkle in their father's eyes.” This expression has a humorous and dreamy feel. Here, the word “twinkle” suggests the interest your father had in your mother.

    When a much older man is interested in a much younger woman and supports her with his money, he is called he “sugar daddy.” The money part is very important-that's the sugar.

    Sometimes fathers are not a good influence or active in the lives of the children. In that case, a person may look for a father figure, a man who is not actually the person's father but who acts like one.

    The relationship between a man and his son can be complex. But the relationship between a father and daughter is often simpler. The expression “daddy's little girl” is understood to mean that, in a father's eyes, his daughter can do no wrong.

    There is usually not a dry eye at any wedding during the traditional father-and-daughter dance, especially if they are dancing to a song like Michael Buble's “Daddy's Little Girl.”

    Diet Coke, diet Pepsi, diet pills, no-fat diet, vegetable diet… We are surrounded by the word "diet" everywhere we look and listen. We have so easily been attracted by the promise and potential of diet products that we have stopped thinking about what diet products are doing to us. We are paying for products that harm us psychologically and physically.

    Diet products significantly weaken us psychologically. On one level, we are not allowing our brain to admit that our weight problems lie not in actually losing the weight, but in controlling the consumption of fatty, high-calorie, unhealthy foods. Diet products allow us to jump over the thinking stage and go straight for the scale(秤)instead. All we have to do is to swallow or recognize the word "diet" in food labels.

    On another level, diet products have greater psychological effects. Every time we have a zero-calorie drink, we are telling ourselves without our awareness that we don't have to work to get results. Diet products make people believe that gain comes without pain, and that life can be without resistance and struggle.

    The danger of diet products lies not only in the psychological effects they have on us, but also in the physical harm that they cause. Diet foods can indirectly harm our bodies because consuming them instead of healthy foods means we are preventing our bodies from having basic nutrients. Diet foods and diet pills contain zero calorie only because the diet industry has created chemicals to produce these wonder products. Diet products may not be nutritional, and the chemicals that go into diet products are potentially dangerous.

    Now that we are aware of the effects that diet products have on us, it is time to seriously think about buying them. Losing weight lies in the power of minds, not in the power of chemicals. Once we realize this, we will be much better able to resist diet products, and therefore prevent the psychological harm that comes from using them.

    While the start of a new school year is always exciting, this year was even more so for some elementary school students in Auckland, New Zealand. They became the world's first kids to be “taught” by a digital teacher, Will. Will is just an avatar(用户头像) that appears on the student's desktop, tablet, or smartphone screen, not a human-like robot walking around the classroom.

    Auckland energy company Vector and AI company Soul Machines worked together to develop Will, which has been modeled after the human brain and nervous system, allowing it to perform human-like behavior. The digital teacher is currently assigned to teach Vector's “Be sustainable with energy,” a free program for Auckland elementary schools.

    Just like the humans it replaced, Will is able to instantly react to the students' responses to the topic. Thanks to a webcam(网络摄像头) and microphone, the avatar not only responds to questions the kids may have, but also picks up non-verbal cues(非口头提示). For instance, if a student smiles at Will, he responds by smiling back. This two-way interaction not only helps capture the students' attention, but also allows the program's developers to monitor their engagement, and make changes if needed.

    Vector's Chief Digital Officer, Nikhil Ravishankar says, “What was fascinating to me was the reaction of the children to Will. The way they look at the world is so creative and different, and Will really captured their attention.”

    Will, in place since August 2018, has been a great success thus far. However, regardless of how popular it becomes, Will is unlikely to replace human educators any time soon. For one, the avatar's knowledge base is severely restricted. But more importantly, even the smartest digital avatars could never predict and react to all the unexpected situations that educators have to deal with on a daily basis. However, it could come in handy as a “personal tutor”, providing kids with one-on-one help on specific subjects or even topics.

    The Winter Olympics is also called the White Olympics. At this time, many colorful stamps are published to mark the great Games. The first stamps marking the opening came out on January 25, 1932 in the United States for the 3rd White Olympics. From then on, publishing stamps during the White Olympics became a rule.

    During the 4th Winter Olympic Games a group of stamps were published in Germany in November 1936. The five rings of Olympics were drawn on the front of the sportswear. It was the first time that the rings appeared on the stamps of the White Olympics.

    In the 1950's, the stamps of this kind became more colorful. When the White Olympics came, the host countries (东道国) as well as the non-host countries published stamps to mark those games.

    China also published four stamps in February 1980, when the Chinese sports men began to take part in the White Olympics. Japan is the only Asian country that has ever held the White Olympics. Altogether 14, 500 million stamps were sold to raise money for this sports meet. Different kinds of sports were drawn on these small stamps. People can enjoy the beauty of the wonderful movements of some sportsmen.

    According to the International Ecotourism Society, eco-travel is "responsible travel to natural areas that protects the environment, maintains the well-beings and involves education". Eco-travel is on the rise, as more and more people become conscious about their carbon footprint.

    Expert from Boundless Journeys, Matt Holmes, who works-on travel experiences towards conserving areas said, "As scientists and non-scientists learn more about how we human beings are impacting the planet, I think more people want to do what they can while still exploring the world. Our guests are definitely interested in that aspect of our journeys. Travelers can farm their own food in Italy, managing their use of water and using solar or wind power. They can also visit n family-run camp that cares for retired logging elephants in Myanmar, know a park entry fee goes to a conservation organization in Costa Rica, employ and train members of the local community or partner with a protection group. There are lots of options for seeking out greener holiday."

    Most people believe that eco-travel is expensive and it is true. Matt explained "Anti-poaching patrols (巡逻) need to be paid, solar energy equipment costs a lot to install, building with environmentally friendly, materials is more expensive and so on. The extra cost is necessary, as you're paying to minimize your footprint and protect the places you visit, which is exactly what eco-travel is about. The financial success and sustainability (可持续性) of an eco- focused operation doesn't come from thin air." The industry is trying to make eco-travel affordable and make it accessible to the common people.